The nation's first lady hits the half-century mark on Friday and, by her own account, she feels more relaxed now that President Barack Obama's days as a candidate are over.

"That layer is gone now. It gives me a little more room to breathe," she told an interviewer.

Nearly five years after assuming the first lady's role following a bruising campaign in which she sometimes became a target, Mrs. Obama is showing increased comfort in what amounts to a volunteer position with a host of responsibilities and outsized expectations. Not to mention a sometimes-unforgiving spotlight.

"I have never felt more confident in myself, more clear on who I am as a woman," the first lady told Parade magazine when asked about the birthday. She started the celebration last week by spending extra time with girlfriends in Hawaii after her family's holiday vacation there. It was an early birthday present from the president. On Saturday, she'll be toasted at a White House party where guests have been advised to come ready to dance, and to eat before they come.

Second presidential terms can be freeing for first ladies, just as they are for presidents, because there is no next election to fret over. But while Mrs. Obama is over the hump of her first lady tenure, with just three years remaining, it's unclear if she will take on new or different roles.

There were expectations last January that she would help the president push for new gun-control measures in response to the shooting massacre of 26 first-graders and adults at a Newtown, Conn., elementary school in December 2012. But she largely avoided the divisive debate after tip-toeing into it during a speech in her Chicago hometown. Mrs. Obama said even less about immigration legislation, another contentious issue and priority for her husband.

Like all first ladies, Mrs. Obama's every move and fashion choices have been closely watched - and mercilessly critiqued. She gets wide credit for carefully shielding daughters Malia and Sasha, now 15 and 12, from the spotlight and for displaying a strong sense of style. But there have been missteps, too, like wearing $500 sneakers to a food bank, taking a pricey vacation to Spain during the economic downturn and being photographed wearing shorts aboard Air Force One.

Still, the more of the public views Mrs. Obama favorably, 59 percent, than her husband, 46 percent, in an Associated Press-GfK poll conducted last month. And she's helped raise millions of dollars for him and other Democratic candidates and has drawn thousands to campaign rallies.

One of her causes that has gained prominence is her campaign to reduce childhood obesity rates. She hopes that work will help define her legacy.

During her husband's first presidential campaign, Mrs. Obama was widely criticized for saying she was proud of her country for the first time in her adult life.

After he was elected, she got back on the public's good side after declaring that her daughters, who were 10 and 7 at the time, were her top priority and she would be "mom in chief." She began to expand her role after settling the girls into their exclusive private school and feeling satisfied that they had adjusted to White House life.

Mrs. Obama planted a vegetable garden on a patch of the South Lawn, the first one there in decades. She used its bounty of sweet potatoes, tomatoes and other crops to begin a national conversation about the country's childhood obesity problem, and the importance of eating right and getting enough exercise. She earned praise and criticism in the process.

School kids were invited to plant, harvest and even make meals with the crops, on the thinking that they are more likely to eat the broccoli if they plant it themselves.

The message has rippled far from that modest start and the first lady can claim some of the credit.

Retailers and food makers are reformulating processed foods to cut down on sugar, salt and fat. Some chain restaurants are making similar changes to what they send out of their kitchens. School lunches are being made healthier and retailers are opening stores in places with limited or no access to fresh food.

Even Sesame Street is allowing the produce industry to use Elmo, Big Bird and its other furry characters free of charge to sell kids on fruits and veggies.

Mrs. Obama once said she's willing "to make a complete fool out of myself to get our kids moving" and has kept her word by doing jumping jacks, kicking soccer balls and dancing the "Dougie" with groups of them to make the point that exercise can be fun. She's even competed in a potato sack race with Jimmy Fallon at the White House and challenged Ellen DeGeneres to a pushups battle on her TV show.

The first lady and Vice President Joe Biden's wife, Jill, a military mom, also lead a nationwide effort to rally the public around military families. Mrs. Obama wrote a best-selling book, "American Grown," about the garden and makes time to advocate for the arts, holding regular music and film workshops at the White House. She and her staff also mentor teenage girls.

The new health care law being one exception, Mrs. Obama rarely makes an overt push for her husband's policies. But she'll begin using her personal story of overcoming obstacles to getting an education to help him meet a previously announced goal of having the U.S. achieve the highest proportion of college graduates in the world by 2020.

The Harvard-trained lawyer has resisted the pressure to advocate causes bolder than childhood obesity and military families.

Robert Watson, who studies first ladies at Florida's Lynn University, said Mrs. Obama probably wants to do more but is reluctant to step out too far because of public distaste for active, assertive first ladies.

"I can't help but think that, before the Obamas leave office, Michelle will take the hand-off from her husband and, head down, go right up the middle for a touchdown," he said.